#697 Merge reload_modules functionality into core

(Mattj on conference/prosody asked me to file this)
Could you consider merging the reload_modules functionalty into core?
Things like letsencrypt force people to reload their certificates much more often than usual. And having mod_tls being reloaded at a SIGHUP is the simplest sotulation to that.
Of course mod_tls could itself hook into config-reloaded and reload the certs only.
reload_modules is a more generic solution, because people can use it for mod_groups too, for example.